H89 inhibitor

Dear all,
I'm trying to use H89 - a PKA specific inhibitor on transfected and
untransfected NIH3T3 cells. I added 5ul of 10mM DMSO solution to 1ml of
medium to reach the final concentration of 50uM. Unfortunately almost all
the cells swim away after 30 min, and I'm not able to fix them on glass
coverslips.
Do you have any hints?
I would greatly appreciate any help,
Marcin
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